Treatment of elongated high speed steel members after austenitizing

ABSTRACT

Elongated members formed of tool steel are maintained straight by sets of aligned rollers during cooling in air through the hardening range between 600* F. and room temperature following cooling after heating throughout to austenitizing temperature. Cooling throughout the hardening range is accelerated by blowing air on the member.

United States Patent Richard F. Erxleben Dearborn Heights;

Orle I. Causley, Fraser, both of Mich. 761,365

July 10, 1968 Sept. 21, 1971 Lear Siegler Inc.

Santa Monica, Calif. Continuation-impart of application Ser. No. 552,944, May 25, 1968, now abandoned.

inventors Appl. No. Filed Patented Assignee TREATMENT OF ELONGATED HIGH SPEED STEEL MEMBERS AFTER AUSTENITIZING 18 Claims, 3 Drawing Figs.

[1.8. CI. 148/ 153, 72/364, 72/366, 148/131 Int. Cl. C21d 1/00, C21d 9/28 Field 01 Search 148/12,

[56] References Cited UNITED STATES PATENTS 1,448,878 3/1923 Smith 148/131 X 3,149,189 9/1964 Gogan 148/131 X 3,169,893 2/1965 Wuerfel. 148/131 3,210,223 10/1965 Good 148/131 3,255,053 6/1966 Bard et a1. 148/131 OTHER REFERENCES The Selection and Hardening of Tool Steels, McGraw Hill Book Co., NY. pages 174- 178 and 193-198 Primary Examiner-Charles N. Lovell Attorney-Whittemore, Hulbert & Belknap ABSTRACT: Elongated members formed of tool steel are maintained straight by sets of aligned rollers during cooling in air through the hardening range between 600 F. and room temperature following cooling after heating throughout to austenitizing temperature. Cooling throughout the hardening range is accelerated by blowing air on the member.

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INVENTOKS 1! RICHARD F. ERXLEBEN CAUSLEY TORNEYS TREATMENT OF ELONGATED HIGH SPEED STEEL MEMBERS AFTER AUSTENITIZING CROSS-REFERENCE TO RELATED APPLICATION BRIEF SUMMARY OF THE INVENTION In the past, considerable difficulty has been encountered in the production of elongated hardened steel members of the type described as a result of distortion resulting from heat treatment including hardening and tempering. Elongated steel members of the character described are ordinarily formed of air-hardening tool steel and a typical steel widely used in the production of such parts in M2 which is an alloy containing both molybdenum and tungsten. This steel is hardened by heating the member throughout to approximately 2200 F., then cooling it in oil or salt to an appropriate temperature as for example 600 F800 F. (for oil), after which the member is permitted to air cool. During the air cooling, during which the member hardens, the broach or other high speed steel member, even if initially straight'when removed from the furnace, undergoes unpredictable distortion which may be relatively great and far beyond acceptable limits. In the past elongated members of this type were straightened during cooling by noting eccentricity or warpage, as for example by rotating the members between centers, and repeatedly reverse bending the members at the points of greatest eccentricity during cooling so as to produce an acceptably straight part.

After the initial cooling, members of this type are ordinarily tempered two or three times by heating to an appropriate tern perature, as for example l,O F., and again permitted to air cool to room temperature. As the elongated members cool, further distortion takes place and the members are straightened repeatedly during cooling by reverse bending as required.

In the past, the air cooling has been gradual and time consuming, but when the present invention is practiced, air cooling can be greatly accelerated by blowing air against the member, thus reducing the air-cooling period surprisingly as much as from 6 to 8 hours to about 2 hours in typical cases.

Even when the greatest of care is exercised, operations as carried out in the past have resulted in occasional breakage or cracking of members. To be within acceptable limits the elongated steel members must have an eccentricity or distortion due to lack of straightness not greater than about 0.010 inch.

With the foregoing in mind, it is an object of the present invention to provide a method of maintaining concentricity or straightness during air cooling through a predetermined temperature range, after heating the member to its hardening temperature and thereafter cooling to an intermediate temperature, which will minimize the requirements for subsequent straightening and eliminate breakage.

It is a further object of the present invention to provide a method of maintaining concentricity during cooling from austenitizing temperature and prior to subsequent tempering or drawing operations which will subsequently reduce the man hours required per piece and which, independently of the foregoing will expedite completion of heat treatment by a substantial amount.

It is a feature of the present invention to mechanically maintain concentricity of the member as it air-cools from an intermediate temperature, by rotating the member on its axis while supporting it at a plurality of points between steady rests, preferably in the form of rollers, adapted to maintain substantially exact concentricity at the zones of support.

It is a further feature of the present invention to control the effectiveness of the maintenance of concentricity by variably predetermining the temperature range throughout which concentricity is maintained.

It is a further object of the present invention to accelerate air cooling from the intermediate temperature by blowing cur rents of air preferably at ambient room temperature, onto the member.

Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings, illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of apparatus employed in carrying out the present method.

FIG. 2 is an enlarged elevational view of a steady rest employed on a lathe bed as seen in FIG. ll.

FIG. 3 is a side elevational view of the steady rest shown in FIG. 2.

DETAILED DESCRIPTION Prior to the present invention a serious problem has been presented by distortion or warping of' elongated high speed or other airhardening steel members during cooling after having been brought to hardening temperature or during cooling after tempering or draw operations. Elongated parts, such for example as broaches, shafts or lead bars were required to be relatively straight when heat treatment was finished, a tolerance of 0.010 inch being permissible in some cases although preferably the part should be maintained straight within 0.007 inch or less.

During the heat treatment an initially straight bar acquires interior stresses and relieves machining stresses, which result in bending, distortion or warping of the bar. This occurs in an entirely unpredictable manner. The bar may during cooling exhibit a uniform bow from end to end. Conversely, it may become S-shaped. In other cases the distortion may appear in different planes so that the bar has a helical distortion.

in the past the method of correcting distortion has been to apply exterior bending stress to the bar so as to reversely bend it where necessary to correct the distortion. If he distortion to be corrected is too great, it is impossible to correct the distortion and there has been an occasional breaking or cracking of parts where the correction was improperly performed by reverse bending. In addition, cooling had to be gradual to avoid cracking or breaking and many man hours were required for the operation.

In order to prevent the accumulation or development of an unacceptably large amount of distortion or bending during the cooling operation, it has been the practice to check straightness of the piece as it cools and where necessary to apply the reverse bending technique to maintain straightness within tolerable limits. Of course, the final straightening during cooling from the final draw or tempering operation has to bring the part to a straightness within the required limits.

In accordance with the present invention a method is employed in which concentrically is maintained only during a critical phase of air cooling following partial cooling from austenitizing temperature. By way of a specific example, broach parts made of M2 steel have been heated to approxi mately 2,200 E, after which they have been quenched in oil to approximately 600-800 or in salt up to 1,050". Following quenching the part is brushed to remove dirt, this operation also removing a copper layer commonly provided by painting prior to initial heating.

The elongated tool steel part is then set up between centers and rotated on its axis. At this time eccentricity or runout, which is due to bending or distortion of the part and which occurred during initial cooling, is noted by indicator. The zones of maximum curvature or eccentricity :are marked. Then rigid steady rest devices which will subsequently be described in detail, are moved into registration with the zones of maximum distortion and are otherwise uniformly positioned along the length of the member at distances which depend upon the dimensions of the part but which may conveniently be from a few inches to two feet or more. These steady rests are moved inwardly simultaneously to engage the high-speed steel member on accurately finished cylindrical surfaces and sufficiently pressure is applied to maintain concentricity of these cylindrical bearing surfaces during continued rotation of the member for a predetermined temperature range during cooling. Cooling is accelerated by directing currents of air preferably at ambient room temperature, over the member. By this step, total time of cooling is materially reduced, and attention of an operator to periodically straighten the member is not required.

Referring now to the drawings, in FIG. 1 there is illustrated apparatus for carrying out the method. A lathe indicated generally at is provided having a driving headstock 12 including a chuck 14 adapted to engage one end of the elongated high-speed steel member M and to drive it in rotation. The other end of the member M is engaged by a center 16 of a tailstock l8. Initially, the lathe 10 is operated to drive the member M in rotation and suitable gauge means are moved along the member M to note the amount and location of distortion. Thereafter, the steady rests, indicated generally at 20, are moved into engagement with the opposite sides of the member, the steady rests being moved axially of the member if desired to insure location of the steady rests at the point of maximum distortion.

Referring now to FIGS. 2 and 3, details of the steady rests are shown.

Each of the steady rests is mounted on base 22 which is movable along ways provided on the bed of the machine and the supports 22 may be firmly clamped in position by suitable means such as the clamp bars 24. Mounted on transversely extending dovetail ways indicated at 26 on each of the supports 22 are a pair of slides 28 and 30, these slides being interconnected by a screw shaft 32 having right-hand screws indicated at 34 and left-hand screws indicated at 36 for causing simultaneous approach and separation between the slides 28 and 30 on rotation of the screw shaft by application of a suitable tool to the squared end 38 thereof.

Extending upwardly from each of the slides 28 and 30 is a rigid column 40 carrying a roll support 42 provided with a pair of rolls 44 and 46. The roll supports 42 are held against the inner surfaces 48 of the column 40 by means including the clamping screw 50. In initial setup a master bar is mounted on the lathe between centers and the slides 34 and 36 are moved inwardly until the rolls 44 and 46 of both supports 42 engage the bar. If engagement occurs between the pair of rolls at one side of the bar prior to the pair of rolls at the other side, the appropriate slide 28, 30 is shimmed to insure exact simultaneous engagement of all four rolls.

In the event that the elongated high-speed steel member to be engaged by the rolls 44 and 46 is relatively heavy, a tie bar 52 is provided which is pivoted as indicated at 54 to one of the columns 40 and which has a threaded portion 56 received in a slot provided at the top of the other column. A clapping nut 58 is provided on the thread portion which may be tightened to insure maintenance of exact concentricity of the portion of the elongated high-speed steel member engaged by the rolls 44 and 46.

By the foregoing operation, if the elongated tool steel member, as is usual, exhibits considerable distortion when initially checked, this distortion is overcome and the part is maintained in a concentric relation during cooling. It is important to note at this time that the operation does not involve reverse bending as has been used in prior practice to correct distortion. If the elongated tool steel member happens to exhibit little or no distortion or to have a portion of its length exhibit substantial concentricity, the support provided by the steady rests prevents distortion during subsequent cooling.

Since the quenching was to approximately 600-800 for an oil quench in the specific example under consideration, the broach or other member, after cleaning and mounting in the lathe and checking to determine distortion, will have cooled usually to a temperature substantially below 600.

It has been found that it serves no useful purpose to position the steady rests to maintain concentricity while the part is above 600". In general, the initiation of maintenance of con centricity is provided at a temperature substantially below 600, in some cases as low as 150 The results are not precisely predictable but in general it is found that if a large runout is noted on the initial check, it is preferable to start the maintenance of concentricity at a lower temperature. On the other hand, other things being equal, maintenance of concentricity will start at a higher temperature for broaches of larger diameter.

Records of a great number of broaches have been maintained and it is found that maintenance of concentricity for a predetermined temperature drop between 600 and F., is effective to reduce the initial distortion by very substantial amounts. Usually, cooling is discontinued at about 125 and the member placed in the furnace for tempering, although cooling to room temperature is possible. In some cases the high point of distortion or eccentricity, marked on the elongated member during the initial checking operation, is moved toward concentricity but fails somewhat short of reaching an exactly concentric position. On the other hand, in some cases the high points are caused to move beyond center so as to produce a condition which may be referred to as reverse bowing or overcorrection. In general it is found that it is preferable to select the temperature range during which concentricity is maintained so as to produce this reverse bowing or overcorrection, since it appears to render subsequent straightening operations simpler.

In the past the initial air cooling following quenching was a gradual operation requiring constant attention of an operator. However, with the present invention in which concentricity is maintained mechanically during a critical range of tempera ture reduction, it is possible and desirable to accelerate air cooling by blowing strong currents of cooling air onto the rotating member. It has been found that in cooling operations normally requiring 6 to 8 hours to reach room temperature, the present method permits cooling to room temperature within 2 hours, and does not require the constant attention formerly required.

It is to be noted that the present method is limited to maintenance of concentricity within practical limits only during a predetermined temperature range of air cooling following initial cooling after the member has been brought to its relatively high austenitizing temperature. During subsequent air cooling following tempering or draw operations, the present method is not employed and the member is maintained with the required straightness by the reverse bending techniques which has previously been employed. It is to be noted however, that this reverse bending technique as applied during the repeated tempering operations is rendered much easier to perform than when the initial hardening operation included manual straightening by reverse bending.

The rate of rotation of the elongated member during the maintenance of concentricity need not be great and excellent results have been obtained when the rate of rotation was at 25 r.p.m., the slowest speed at which a lathe on which the operation has been performed can be run. The speed of rotation is evidently not critical but should be between about l0 r.p.m. and a few r.p.s.

EXAMPLE In the following examples, the procedure used was as follows: The elongated members were brought up to the appropriate temperature as for example 2,200 F., and were quenched in oil to the temperature noted. The parts were removed from the oil and placed between centers on a machine with adjustable steady rests about 12 inches apart. The members were rotated at 25 r.p.m. and the steady rests tightened. The members were allowed to cool from the temperatures listed as straightening temperature (Straightening Temperature) to 125 F. and sometimes to ambient temperatures and then put in the tempering furnace and the regular heat-treating cycle was continued, with the results noted.

Maximum runout after- Straight- Quench ening Stralght- First temperatompara- Quench enlng, draw, Slze, inches ture, F. ture, F. inches inches inches 1.954 x 80 800 250 145 030 .030 2.143 x 67 800 300 095 .020 026 2.317 x 58% 650 250 .105 .007 .010 3. 223 x 67 916 650 275 110 016 .030 3. 378 x 79% 650 375 .160 .020 .020 3. 378 x 79% 650 250 .125 015 .030 3. 644 x 72 650 300 .130 .010 .020 4. 196 x 80 800 325 105 007 030 4. 213 x 74 800 325 .095 .010 .040 4. 679 x 81 264 800 325 .220 020 035 4. 770 x 80 800 360 110 015 040 4.770 x 80 800 260 145 .018 .040 5. 390 x 80 800 400 080 .012 .035 4. 779 X 58 800 400 065 005 025 It is noted that austenitizing temperature of the alloys Tl, M2 and M3 are above 2,150 F.

While the foregoing examples include Tl, M2 and M3 steels, the invention is applicable generally to air-hardening tool steels. These steels are heated throughout to austenitizing temperature in excess of 2,000 F. and are then ordinarily cooled as for example by quenching in oil or salt to much lower temperatures, for example 600-800 P. if quenched in oil. At these temperatures the material of the elongated members is still plastic and appreciable hardening has not commenced. As these steel thereafter are allowed to cool relatively slowly in air, the hardness increases and it is during this stage of cooling that distortion occurs.

The steels to which the present invention is applicable may be described generally as air hardening tool steels including high-speed tool steels. Specifically, the steels to which the present invention is applicable are A2-l0; D l-7; l-ll026, 41- 43;Tl9,l5;Ml-4,6-8,10,15,30, 33-36,4l-44.

It will be noted that the present method of maintaining concentricity by the roll steady rests eliminates all of the man hours involved in straightening the elongated member out of quench. All that is required is for the operator to place the member in the machine, tighten the roll steady rests, and start the member rotating. The method apparently results in the elongated members being straightened relatively stress free in that the runout developed after the first tempering operation is reduced substantially compared to runout which would be anticipated without practice of the present invention.

It will be noted from the foregoing that the step of mechanically maintaining straightness of the part takes place mainly in the transformation range, which for a typical steel such as M2, starts below 500 F.

The invention is applicable to any size part, but its advantages are best realized with larger parts, as for example 36- inch or longer and about 2-inch diameter or more. This is due in part to the fact that on smaller parts which cool more rapidly, the man hours required to maintain straightness by conventional processes are substantially less than on larger parts.

It will be understood that the cooling may include any recognized quenching operation such as cooling oil, in salt followed by air cooling to room temperature, or even air cooling alone.

While the theoretical explanation of the results achieved is not fully understood, it has been found that the rotation of the part during the maintenance of straightness during a predetermined portion of cooling contributes substantially to the greatly improved results obtained, and equivalent results are not obtained by maintaining straightness or concentricity without rotation.

The drawings and the foregoing specification constitute a description of the improved treatment of elongated highspeed steel members after austenitizing in such full, clear, concise and exact terms as to enable any person skilled in the art to practice the invention, the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. The method of treating elongated members of air-hardening tool steel having aplurality of longitudinally spaced axially aligned annular zones thereon which comprises heating the members throughout to austenitizing temperature, cooling the members to a predetermined intermediate temperature between 600 and 150 F. without checking or maintaining straightness, and thereafter air cooling the members at least to F. while maintaining a plurality of axially spaced zones of said members in substantially exact concentricity during cooling throughout the air hardening range by the step of supporting annular zones on the members in concentric aligned positions between supports mounted in fixed position and rotating the members.

2. The method of claim 1 in which each of said supports comprises at least three rollers.

3. The method of claim 1 which comprises the step of directing a current of cooling air at room temperature against the members during cooling thereof.

4. The method of claim 2 which comprises the step of directing a current of cooling air at room temperature against the members during cooling thereof.

5. The method of claim 3 which comprises initiating the maintenance of concentricity at a temperature between 425 F. and 225 F.

6. The method of claim 5 which comprises continuing the maintenance of concentricity to a temperature near 125 F.

7. The method of claim 5 which comprises discontinuing the maintenance of concentricity at room temperature.

0. The method of claim 3 which comprises rotating the members at a speed of between 10 rpm. and a few r.p.s.

9. The method of claim 1 which comprises thereafter tempering the members and straightening them to maintain the required tolerance by reverse bending during cooling.

10. The method of claim 1 which comprises indicating eccentricity of the members during initial rotation, and applying the maintenance of concentricity at the zones initially exhibiting maximum eccentricity.

11. The method of claim 1 in which said members are formed of alloy steels selected from the group consisting of M2, M3 and Tl.

12. The method of claim 1 in which said members are formed of M2 alloy steel.

13. The method of claim 11 in which said members are broaches.

141. The method of claim 12 in which said members are broaches.

15. The method of claim 4 in which said members are short, and in which said rollers have their axes parallel to the length of the members and support the members without axial ad- 1 vance until their temperatures fall to about 125 F.

16. The method of heat treating an elongated broach of generally circular cross section having at longitudinally spaced zones therealong a plurality of axially aligned annular zones, the broach being formed of an air-hardening steel alloy selected from the group consisting of T1, M2 and M3, the method comprising the steps of heating "the broach throughout to tis austenitizing temperature in excess of 2,l50 F. cooling the broach to an intermediate temperature between 600 F. and F. without checking or maintaining straightness, thereafter supporting the broach with the annular zones maintained in exact axial alignment by sets of at least three rollers r broach, rotating the broach by rotating one or more of said rollers, directing a current of cooling air over substantially the entire surface of said broach during its rotation by said rollers, and continuing the maintenance of aligned rotation, and the direction of cooling air against the broach until its temperature has fallen to a temperature between 125 F. and room temperature, and thereafter tempering said broach in a tempering operation in which the straightness of the broach is maintained within limits during air cooling by reverse bending.

17. The method as defined in claim 1 which comprises mounting the members for rotation on a fixed axis after cooling to the aforesaid intermediate temperature, rotating the members to determine zones of maximum eccentricity, and positioning at least some of the supports longitudinally of said members into substantial registration with zones of maximum eccentricity.

187 The method as defined in claim 16, which comprises mounting the broach for rotation on a fixed axis after cooling to the aforesaid intermediate temperature, rotating the broach to determine zones of maximum eccentricity, and positioning at least some of the sets of rollers longitudinally of the breach into substantial registration with zones of maximum eccentricity. 

2. The method of claim 1 in which each of said supports comprises at least three rollers.
 3. The method of claim 1 which comprises the step of directing a current of cooling air at room temperature against the members during cooling thereof.
 4. The method of claim 2 which comprises the step of directing a current of cooling air at room temperature against the members during cooling thereof.
 5. The method of claim 3 which comprises initiating the maintenance of concentricity at a temperature between 425* F. and 225* F.
 6. The method of claim 5 which comprises continuing the maintenance of concentricity to a temperature near 125* F.
 7. The method of claim 5 which comprises discontinuing the maintenance of concentricity at room temperature.
 8. The method of claim 3 which comprises rotating the members at a speed of between 10 r.p.m. and a few r.p.s.
 9. The method of claim 1 which comprises thereafter tempering the members and straightening them to maintain the required tolerance by reverse bending during cooling.
 10. The method of claim 1 which comprises indicating eccentricity of the members during initial rotation, and applying the maintenance of concentricity at the zones initially exhibiting maximum eccentricity.
 11. The method of claim 1 in which said members are formed of alloy steels selected from the group consisting of M2, M3 and T1.
 12. The method of claim 1 in which said members are formed of M2 alloy steel.
 13. The method of claim 11 in which said members are broaches.
 14. The method of claim 12 in which said members are broaches.
 15. The method of claim 4 in which said members are short, and in which said rollers have their axes parallel to the length of the members and support the members without axial advance until their temperatures fall to about 125* F.
 16. The method of heat treating an elongated broach of generally circular cross section having at longitudinally spaced zones therealong a plurality of axially aligned annular zones, the broach being formed of an air-hardening steel alloy selected from the group consisting of T1, M2 and M3, the method comprising the steps of heating the broacH throughout to tis austenitizing temperature in excess of 2,150* F. cooling the broach to an intermediate temperature between 600* F. and 150* F. without checking or maintaining straightness, thereafter supporting the broach with the annular zones maintained in exact axial alignment by sets of at least three rollers in contact with each of a plurality of selected annular zones, said rollers having their axes parallel to the length of the broach, rotating the broach by rotating one or more of said rollers, directing a current of cooling air over substantially the entire surface of said broach during its rotation by said rollers, and continuing the maintenance of aligned rotation, and the direction of cooling air against the broach until its temperature has fallen to a temperature between 125* F. and room temperature, and thereafter tempering said broach in a tempering operation in which the straightness of the broach is maintained within limits during air cooling by reverse bending.
 17. The method as defined in claim 1 which comprises mounting the members for rotation on a fixed axis after cooling to the aforesaid intermediate temperature, rotating the members to determine zones of maximum eccentricity, and positioning at least some of the supports longitudinally of said members into substantial registration with zones of maximum eccentricity.
 18. The method as defined in claim 16, which comprises mounting the broach for rotation on a fixed axis after cooling to the aforesaid intermediate temperature, rotating the broach to determine zones of maximum eccentricity, and positioning at least some of the sets of rollers longitudinally of the broach into substantial registration with zones of maximum eccentricity. 